This invention relates generally to electronic data processing systems, and more particularly to the method of addressing and accessing stored data in a data processing system employing paged memory.
The use of paging techniques for data storage is known in the data processing art, particularly in large computer systems such as the Honeywell 6800 Multics System which utilizes multiple processors and permits multiple programming and concurrent system users. Paging permits the storage of data and programs in bulk storage devices (e.g. disk or tape units) with required data and program portions called into main memory as required for program execution. Advantageously, the "virtual memory" seen by a system user actually includes the bulk storage along with main memory through use of the paging mechanism, thus minimizing the required size and attendant cost of main memory.
In copending application Ser. No. 562,317, supra, an input-output processing system is disclosed which has paged memory capabilities. The present invention is directed to the paged memory capabilities and particularly to the method of generating addresses to the paged memory.
Accordingly, an object of the present invention is a method of generating addresses to a paged memory.
Another object of the invention is a method of developing absolute memory addresses and effective memory addresses for paged memory.
Still another object of the invention is a method of addressing paged memory including the use of page table words and effective addresses to develop absolute memory addresses.
A feature of the invention is the use of a page table word scratchpad memory having a plurality of levels corresponding to priority levels of processes.
Another feature of the invention is the use of least significant bits of a page number to access space in the page table word scratchpad memory.